Steam generation



March 28, 1961 A. T. HUNTER Erm. 2,976,853

STEAM GENERATION Filed March 51, 1959 2 Sheets-Sheet 1 ARTHUR T. HUNTERROBERT C. PATTERSON EVERETT C. LEW|$ ATTORNEY March 28, 1961 A. T.HUNTER Erm. 2,976,853

STEAM GENERATION Filed March C51, 1959 2 Sheets-Sheet 2 INVENTORS:ARTHUR T. HUNTER ROBERT C. PATTERSON EVERETT C. LEWIS Unit States STEAMGENERATION Filed Mar. '31, 1959, Ser. No. 803,305 4 Claims. (Cl. 122-4)This invention relates to an improved method for generating and/ orheating steam or for heating other desired fluids and has particularrelation to an improved method for this purpose employing a uidized bedwithin which fuel and air are introduced with the fuel being oxidizedwithin the bed and with the `fluid to be heated passed in indirect heatexchange relation with the bed.

A bed of discrete material may be fluidized by passing a stream of gasupwardly therethrough, with uidization for a particular particle sizeoccurring at or above a predetermined velocity and temperature. When inthis fluidized state the particles of the material move rather rapidlythroughout the body of material with the entire mass being in anagitated state resembling a boiling liquid and with the violence of theagitation depending upon the velocity of the gas passing upwardlythrough the material. When in this iluidized state the material is notcarried along with the iluidizing gas and although the body of materialwill be expanded from its packed or nonfluidized condition, the uidizinggas passes through the material and leaves the same at what is termed adisengaging zone. With a given particle size and density the velocity ofthe gases passing through the material must be maintained lwithinspecific minimum and maxi.

mum limits in order to have proper fluidization. The maximum limit isthat where substantial quantities of the material are carried away fromthe bed in the gas stream, or in other words, the material is entrainedwithin the gas stream, while the minimum limit is that below whichfluidization does not occur, the mass of material remaining in theso-called packed condition and the particles not moving from their atrest position.

It is well recognized that within fluidized beds an extremely high rateof heat transfer prevails among the lluidizing gas, the lluidizedparticles and a heat exchange coil or the like immersed within the bed.In addition to this high rate of heat transfer, which is many times thatobtained with conventional systems, i-t has been found that by injectingfuel and air directly into a liuidized bed and oxidizing the fueltherewithin very high heat release rates are obtainable which are manytimes those obtainable by conventional firing methods. These characteristics render the use of liuidized beds within which atent thegenerating and/ or heating of steam or the heating of other desiredluids because of the great reduction in size of equipment over thatheretofore required for accomplishing the same result.

It has been found desirable, for severalA reasons, to operate these bedsin the neighborhood of l800 F. or within the range of 1600 to 2000 F. Atthis temperature complete oxidation of commercially feasible fuels,which have relatively high ignition temperatures is had with a bed ofmaterial that is not as costly, extremely active oxidation catalyst butwhich can be obtained very economically and will not catalyze theoxidation process at a temperature substantially below thesetemperatures but does catalyze the process at these rather hightemperatures. Materials such as activated alumina, tubular alumina andthe like have proved satisfactory for such beds. The working fuelsreferred to have an ignition temperature of from 1000 to 1400" F. and itis found that with a bed temperature somewhat above the ignitiontemperature such as the 16002000 F. range mentioned satisfactoryoxidation is obtained. Another result of operating at these hightemperatures is the attainment of very high heat transfer rates, muchhigher than at lower temperatures, with 50-55 B.t.u./sq. ft./ F.differential being obtained with a particle size of about 1A; inch andapparent density of 60 lbs. per cubic ft., with there being no seriousmetallurgical problems experienced with regard to the tube coil immersedwithin the bed since this coil is adequately cooled by the iluid flowingthrough it so as to keep its temperature below an excessive value.

While With these economic materials satisfactory oxidation of a mixtureof such a working fuel and air is had when the bed of material is in thetemperature range of 1600-2000 F. there exists the very diicult problemof heating the bed of material to this high temperature in a simple,economical and feasible manner. The present invention is directed to thesolution of this problem.

In accordance with the invention there is provided a bed of material,such as activated alumina which is heated to a temperature sufficientlyhigh to oxidize an ignition fuel which as a much lower ignitiontemperature than the commercially feasible working fuel and at whichtemperature the bed of material is incapable of oxidizing the workingfuel. This heating of the material may be accomplished by passing hot.air upwardly therethrough with the air being heated by means of aspecial air heater which may take the form of a duct burner. It ispreferable, although not necessary to maintain the bed in a packedcondition during this heat-up period so that the rate of heat transferto the coil is at a low value. After thus heating Ithe bed of materialthe ignition fuel is introduced thereinto and air is passed upwardlytherethrough with this ignition fuel being oxidized within 'the bed ofmaterial. Sucient of this ignition fuel is introduced into the bed sothat the heat evolved by its oxidation will raise the temperature of thebed to where the working fuel will be effectively oxidized or in otherwords, to the 1600-2000" F. range. Thereafter the supply of ignitionfuel to the bed is stopped and the Working fuel is introduced thereintoalong with air being passed upwardly through the bed with the gas flowthrough the bed being regulated Ito maintain the bed -uidized Theworking fuel is completely oxidized within the bed (complete oxidationmeaning only minute traces of unburned fuel being evidenced in theefluent from lthe bed) and heat is impaited to a luid, such asconverting water to steam by passing it in indirect heat exchangerelation with the bed with a tube bundle or the like being immersed withthe bed for this purpose.

In a modification of this method a still lower preheating is had byutilizing a bed of material that is a very active oxidation catalyst. Inthis modification a separate bed is provided and into which the ignitionfuel is introduced with this separate bed being comprised at least inpart of a very active oxidation catalyst. This bed is heated, as by hotair, to a temperature sulciently high to elect ,oxidation of the lowignition temperature ignition fuel and the hot eluent from thiscatalytic bed is passed through the main bed to heat it to its requiredtemperature for oxidizing the working fuel with the working fuel thenbeing supplied to this main bed, the ignition fuel turned off and themain bed maintained fluidized as in the previously describedembodiment.-

It is an object of this invention to provide an improved method for thegenerating and/or heating of steam or other desired'uids employingalluidized bed..

of material within which fuel is introduced and burned and from whichheat is absorbed to heat the desired lluid.

Fig. l is -a diagrammatic representation in the form of a verticalsection through an apparatus suitable for carrying out one form of themethod of the invention,

Fig. 2 is a sectional view taken along line 2--2 of Fig. l.

Fig. 3 is a view similar to that of Fig. 1 but showing a modifiedapparatus suitable for carying out another form of the method oftheinvention.

Referring now to the drawing, wherein like reference characters are usedthroughout to designate like elements, the stnuctural organizationdiagrammatically represented in Figs. 1 and 2, comprises ahousing 10into the lower end of which is introduced air or other suitablecombustion supporting gas, with fan or pump 12 forcing this air into andupwardly through the housing with the air prior to its entrance into the4housing passing through preheater 14, of any desired construction,where it is preheated as required. g

Within housing there is disposed an upper mass or bed of discretematerial 16-and a lower mass or bed of discrete material 18 which isseparated from the upper bed being 'supported on a perforated plate orclosely spaced tubes 20 while the lower bed is supported on a similarperforate plate or closely spaced tubes 22 with each of these platespermitting a gas to pass upwardly throughthem and accordingly throughhousing 10 while preventing the passage of the material which theysupport downwardly through them. The upper plate or tubes 20 must becooled in order to withstand the high temperature to which they aresubjected and accordingly if a plate is'employed cooling tubes areattached to it while if tubes are employed a Vcooling medium is passed-through them.

In lieu of separating material'lslfrom material 16 by plate or tubes 20the vparticles of` material 18 may be of suiciently greater size ordensity than those of the mate rial 16 so that they do not uidize withinthe range of fluidization lvelocity of the material 16 whereby material18 will remain in the lower endof housing 10 with maferial 16 disposed'immediately thereabove and restingY thereon.

The'bed of material 18 is comprised at least in party of a very activeoxidation catalyst such as activated alumina coated or impregnated withplatinum, palladium, rhodium,v ruthenium, silver, copper, chromium,manga-7 nese, nickel,l cobaltor combinations of these metals while thebed 'ofnlaterial '16 is comprised of a material which is "much VlessVALactive as `an oxidation catalyst and is accordingly much more'economical such as activated alu-` mina, per se, or tubular alumina.Fuel may be intro,1 duced into each ofthese beds with the fuel beingintroduced into the lower portion of bed y18 through the distributionconduits 24 which are connected to lieaderk26` supply headerv38`a1idreturn header 40. Fluid to be heated is conveyed through thetube bundle and this bundle may advantageously take the form of a steamgenerator wherein water is'evaporated. The tube bundle may bee'modied toyform or include part or all of the walls of the enclosure or housing10.

The so-called working fuel lfor vthe organization of Figs. 1 and-2 issuppliedto header 3i) and introduced into the lower portion-of bed 16.through the distribution foonduits 28. Thisffu'el is Yexrployedlforsustained operation f' of the device and as previously mentioned fuelsthat are economically feasible have a characteristically high ignitiontemperature. Therefore an ignition fuel which is employed only duringthe starting-up periods of the unit is introduced into the bed 18through distribution conduits '24 with this ignition fuel having asubstantially lower ignition temperature than that of the working fuel.When operation of the unit is initiated the air that is forced upthrough housing 10 and accordingly through the beds 18 and 16 by meansof the fan 12 is preheated by air preheater 14 sufliciently to heat thebed of very active catalyst 18 to a temperature somewhat about itsactivation temperature for the ignition of the fuel. Thereafter valve 32is opened and this ignition fuel is introduced into the bed 18 where itis oxidized. The eiiluent from this bed -18 passes upwardly through thebed 16 and the supply of ignition fuel to the bed 18 is regulated sothat this effluent will heat the material in bed 16 to a suiciently hightemperature that it is capable of oxidizing the working fuel whenintroduced thereinto from 'distribution conduits 28 and with the gas owthrough bed 18 preferably being maintained below that required foruidization during this heating period. When the material in bed 16 is soheated valve 32 is closed and valve 34 is opened so that the supply ofignition fuel to bed 18 is shut olf and the Working -fuel is supplied tothe lower portion of bed 16. Since bed 16 has been heated suiciently tooxidize this working fuel the fuel lwill be oxidized within this bed ofmaterial. The passage of air upwardly through the bed of material isthen `regulated so that the bed is maintained iu a liuidized state andthe heat evolved or a portion ofthe heat evolved from the oxidation ofthe working fuel within the bed is imparted to the iluid that isconveyed through the heat exchange bundle 36.

By the use of an ignition fuel which has an ignition 'temperaturesubstantially lower than that of the working fuel and by the use of abed of very active oxidation catalyst which accordingly has a lowactivation temperature or minimum temperature at which it is capable ofoxidizing `a fuel and into which the ignition fuel is introduced thecapacity that is required for the 'preheater 14 is Ysufficiently low sothat from an economic standpoint it is within reason and is feasible.

In accordance with this method the following opera tion has been carriedout. When methane was employed as Lthe working fuel, which has anignition temperature of approximately 1200" F., an ignition fuel was'ernployed which had an ignition temperature of approximately 500 F. andwas introduced into a bed of catalyst which was capable of oxidizingthis ignition fuel at a temperature of 600-700 F. The bed of catalystwas heated to a temperature within this range and the ignition fuel thensupplied to the catalyst. The supply of this fuel was regulated so thatthe effluent from this bed of catalyst heated the `bed of material 16 toa temperature generally within the range of l600-2000 F. at

which temperature this material was capable of completely oxidizing theworking fuel. When this temperature was obtained the supply of ignitionfuel to the bed of catalyst 18 was terminated and the working fuel wassupplied to the bed of material 16 with Ithis bed being maintained in afluidized condition and with complete oxidation of `the working fuelbeing had within this bed.

In the modiiication represented in Fig. 3, in lieu of employing abed ofcatalyst a single bed (16a) of material is employed which is comprisedof the previously mentioned economical material that is capable ofoxidizing the working fuel to produce complete lcombustion only at therather high temperatures mentioned with the ignition fuel beingintroduced into the lower portion of this bed through distributionconduits 28a. The operation of this organization is lsimilar to thatpreviously described except that the bed of material'16a "must be heatedto a'temperaturesuihciently' high to oxidizethe ignition fuel with thistemperature of course being somewhat higher than that required when avery active oxidation catalyst is employed `as in the previouslydescribed embodiment although it is substantially lower than thatrequired to oxidize the working fuel and has been found p to be lowenough to render the operation commercially feasible. When the bed ofmaterial has been heated to this required temperature by means of airheater 14 the ignition fuel is introduced into the lower portion of thebed through distribution conduits 24a with this fuel being oxidizedwithin the bed and with the heat evolved heatying the bed to asuiciently high temperature so that it is capable of oxidizing theworking fuel. Thereafter the supply of ignition fuel is terminated andthe working fuel is introduced into the -bed and completely oxidizedtherewithin with the gas ow upwardly through the bed being regulated tomaintain the bed fluidized.

With this modified form of method, operating with methane (ignitiontemperature 12.00 F.) and with an ignition fuel having an ignitiontemperature 500 F., the bed of material 16a was heated by means of hotair to a temperature of between 80G-900 F. after which the ignition fuelwas introduced thereinto and completely oxidized or substantially`oxidized therewithin. The supply of ignition fuel Was regulated so thatthe bed was heated to between 1600-2000 F. after which the supply ofignition fuel was terminated and the working fuel was supplied to thebed, the bed iluidized and with oxidation of the working fuel beingeffected in the bed and with the working fuel being regulated tomaintain the temperature of the bed within this range.

Thus in accordance with the present invention the heating of a bed `ofmaterial to the high temperature required for oxidation of acommercially feasible fuel which has a high ignition temperature isgreatly simplified and brought within the realm of reality with themethod being highly practicable and highly satisfactory and overcomingan extremely difficult problem in starting units to which the inventionis directed.

The term air as used through the application includes all combustionsupporting gases and gas mixtures.

This description is intended for the purpose of explanation andillustration only and is not to limit the invention since manymodifications which are within the scope and spirit of the inventionwill occur to those skilled in the art. Y

What is claimed is:

l. The method of steam generation through oxidation of a working fueland transfer of heat to water which comprises heating a stream of air toa temperature below the ignition temperature of the working fuel butabove the ignition temperature of an ignition fuel which has an ignitiontem-perature well below that of the Working fuel, passing said airupwardly through a ybody of discrete material at a suflicient-ly lowvelocity so that the material does not uidize and thereby heating thesame to a temperature above the ignition temperature of theignitionfuel, thereafter introducing said ignition fuel into said bodyof material and oxidizing the same therewithin, utilizing a portion ofthe heat thus liberated to heat a body of discrete material to atemperature well above the ignition tempera-ture of the working fuel,and Where the material will effect substantially complete oxidation of amixture of the working fuel and air that is introduced thereinto, afterthis body of material attains this desired temperature introducing sucha mixture into and passing it upwardly through this body of material andterminating he flow of said ignition fuel, regulating the gas flowthrough the 'body of material so as to lluidize the same and completelyoxidize the working fuel within said iluidized lbody of material, andconverting' Water to steam by passing it in indirect heat exchangerelation with this iluidized body of material.

2. The method of uid heating through oxidation of a Y when heated to agiven temperature much lower than said predetermined high, heating theair prior to its passage through the bed sufficiently to raise thetemperature of the bed incident to passage of the `air therethrough to apoint where it is capable of effecting oxidization of the ignition fuelbut incapable of effecting oxidation of the working fuel, thereafterintroducing said ignition fuel into the lower portion of the bed andoxidizing the same therewithin, regulating the supply of fuel and air tomaintain the bed packed and impart sufficient heat to the bed to raiseits temperature to atleast said predetermined high, thereafterintroducing said Working fuel into the bed, increasing the air flowtherethrough to uidize the bed and terminating the introduction of theignition fuel thereinto, substantially completely oxidizing said workingfuel within said bed, imparting heat to a uid by passing it in indirectheat exchange relation with the fluidized bed, and regulating the supplyof said Working fuel to maintain said bed of material at a temperatureat least as high -as said predetermined high temperature.

3. The method of fluid heating through oxidation of a working fuel andtransfer of heat to -a lluid comprising passing air upwardly through abed of material which is capable of effecting substantially completeoxidation of the working fuel when the material is heated to apredetermined high temperature and of an ignition fuel when heated to agiven temperature much lower than said predetermined high with thisgiven temperature being generally in the range of G-900 F., heating theair prior to its passage through the bed sufliciently to raise ignitionfuel into the lower portion of the bed and oxi` dizing the sametherewithin, regulating the supply of fuel and air to maintain the bedpacked and impart sufficient heat to the bed to raise its temperature toat least said predetermined high, thereafter introducing said workingfuel into the bed, increasing the rair flow therethrough to iluidize thebed :and terminating the introduction of the ignition fuel thereinto,substantially completely oxidizing said working fuel within said bed,imparting heat to -a fluid by passing it in indirect heat exchangerelation with the iluidized bed, and regulating the supply of saidworking fuel to maintain the temperature of said bed of material atleast as high as said predetermined high temperature.

4. The method of uid heating through oxidation of a working fuel andtransfer of heat to =a fluid comprising passing air upwardly through abed of material which is capable of effecting substantially completeoxidation of a working fuel having an ignition temperature ofapproximately 1200 F. when the material is heated to a temperaturegenerally in the range of 1600-2000" F. and an ignition fuel having anignition temperature of approximately 500 F. when the material is heatedto a temperature generally in the range of 800 to 900 F., heating theair prior to its passage through the bed sufficiently to raise thetemperature of the bed incident to passage of the air therethrough to atemperature generally in the range of SOO-900 F., thereafter introducingsaid ignition fuel into the lower portion of the bed and oxidizing thesame therewithin, regulating the supply of fuel and air to maintain thebed packed and impart suliicient heat to the bed so that its temperatureis generally in the range of 1600-2000" F., thereafter introducing saidworking fuel into the bed, increasing the air ilow therethrough tu'idize the bed vand terminating the introduction of the References.ACited inthe leof this patent ignition 'fuel' thereinto, substantiallycompletely oxidiz- UNITED- STATESV-PATENTS f fidby'pass'ing it inindirect heat exchange relation with 420056 Hackney "j Ian' 28 'f1890 YY Y. 2,664,346 Mayhew Dec.29, 1953 the uidized bed, `and regulating thesupply of said work- 5 l ing fuel to maintain said bed of material at atempera- FOREIGN PATENTS 4 ture generally in the range of x1600-2000 F.7922682 ",Great Britain Api-Q2; `14958

